1. Field of the Invention
The present invention relates to power wrenches and more specifically to power tongs for making up and breaking out threaded connections between adjoining tubular members. In particular, the invention relates to a mechanism for bringing the gripping elements of an open mouth power tong into secure and uniform engagement with the pipe so that the pipe may be rotated evenly about its axis.
2. Description of the Prior Art
Oil field tubular members, e.g. drill pipe and casing, are employed in sections which are joined together at their ends by threaded connections. Power tongs of the type herein described are utilized to make and break out these threaded connections by securely gripping one tubular member and rotatably driving that member relative to the adjoining member.
Power tongs representative of present practice in the industry are described in U.S. Pat. Nos. 2,879,680; 3,180,186; 3,261,241 and 4,084,453. It has been found that the camming action typically used to bring the gripping elements or dies into contact with the pipe results in frequent misalignment of the pipe relative to the center of rotation of the tong. That is, the pipe often is not rotatably driven about its axis. This misalignment and the resultant vibrations place a severe limitation on the rotational speed which may be imparted to the pipe and, in extreme cases, may result in damage to the pipe or tong and a safety hazard to the operator. Thus, there is a need for a power pipe tong having means for securely and uniformly engaging the pipe in such a manner that the pipe may be rotated evenly about its axis.